Gas Pressure Testing and Leak Detection

Why Pressure Testing Matters

Before any gas piping is concealed behind walls, ceilings, or underground, it must be tested to prove it holds pressure without leaking. This step protects lives. Natural gas and LP (liquefied petroleum) gas are both flammable and, in sufficient concentration, explosive. A single undetected leak left inside a wall cavity can accumulate to dangerous levels over days or weeks. Pressure testing and leak detection are the last line of defense before the system is hidden from view, and no authority having jurisdiction (AHJ) will approve covering work that has not passed a documented pressure test.

This lab follows the testing procedures outlined in the International Fuel Gas Code (IFGC), which most US states adopt (sometimes with local amendments). Always confirm the exact requirements with your local AHJ and the adopted edition of the code in your jurisdiction.

Test Medium: Why Air, Not Gas

During rough-in testing, air — not gas — is always used as the test medium. Air is non-flammable. Using actual gas to pressure-test new piping before the system is verified leak-free would create a serious explosion and fire hazard. An air compressor with a regulated low-pressure output supplies the test pressure. Do not use oxygen or any other industrial gas; use only clean, dry air or an inert gas such as nitrogen.

Test Pressure and Hold Time

The IFGC specifies minimum test pressure and hold time requirements for gas piping. Requirements vary based on pipe size, operating pressure of the system, and whether the piping is new or being extended. For typical residential and light-commercial gas piping (systems operating at pressures of one-half pound per square inch or less), the IFGC requires a minimum test pressure and a minimum hold time — consult your current IFGC reference for the exact values that apply to the pipe size and system type you are testing. Always record the specific code edition and section on your test record form.

The pressure gauge you use must be calibrated and appropriate for the test pressure range. A gauge with too large a range may not show a small pressure drop clearly. Read and record the gauge at the beginning and end of the hold period. If the final reading equals the initial reading (within the tolerance of the gauge), the system passes.

Equipment Setup

1. Cap all open ends of the piping assembly.

2. Install the pressure gauge at a convenient access point (often a capped tee or test port).

3. Connect the regulated air supply and slowly bring pressure up to the required test pressure. Do not overpressure the assembly.

4. Isolate the air supply (close the supply valve) before beginning the timed hold period. The gauge reading should remain stable.

5. Start the timer. Watch the gauge throughout the hold period.

Leak Detection with Detection Solution

Gas leak detection solution (sometimes called bubble solution) is a liquid applied to joints, fittings, and connections with a brush or applicator. If air is escaping from a joint, it will cause the solution to bubble. Apply solution generously to every joint — threaded connections, union fittings, valves, and any other assembly points. Watch each joint for 15–30 seconds before moving on.

A slow leak may produce very small, slow bubbles; do not rush. If you find a leak:

• Mark the location.
• Release the system pressure before making any repairs. Never tighten a fitting or make repairs while the system is under pressure.
• Correct the defect (tighten the fitting, re-apply thread sealant, or replace the fitting as needed).
• Re-pressurize and re-test the entire system. The test clock restarts.

Electronic combustible gas detectors are used to detect gas leaks on live systems, but during an air pressure test, the detection solution method is the standard approach because the test medium is air, not combustible gas.

Safety Rules for This Lab

• Eye protection (safety glasses or goggles) is mandatory whenever the system is pressurized.
• Keep bystanders clear of capped ends; a cap that is not fully engaged can become a projectile.
• Never exceed the test pressure. Set the regulator before pressurizing.
• Lockout/tagout (LOTO) procedures apply to the air compressor when work is being performed on the assembly (repairs, fitting changes). De-energize and tag the compressor before touching any fitting.
• Do not use open flames, sparks, or heat sources near any test assembly, even though the test medium is air, because residual gas contamination may be present in field situations.
• Inspect the pressure gauge before use. A cracked lens or damaged Bourdon tube is unsafe; swap it for a serviceable gauge.

Completing the Test Record

Documentation is as important as the test itself. An inspector must be able to read your record and confirm every required parameter was met. Your form must include:

• Pipe size and material
• Test medium (air)
• Test pressure (recorded value)
• Required hold time and actual hold time
• Initial gauge reading and final gauge reading
• Leak findings (location, description)
• Corrective action taken (or "no leaks found")
• Your name, date, and instructor sign-off

Incomplete forms will not be accepted. In the field, an incomplete or missing test record can result in a failed inspection and required re-inspection fees. Treat every form as a legal document.

Connection to Your Credentials

NCCER Plumbing Levels 3 and 4 include gas piping installation and testing. Journeyman licensing exams in most states include questions on gas system testing procedures and code requirements. Accurate test documentation is also a professional and legal obligation once you are licensed.